Viruses are key components of marine ecosystems; however, the temporal dynamics, diversity and variability of viruses in these ecosystems are not well understood. The authors surveyed the diversity and temporal dynamics of viral assemblages over daily and seasonal timescales in waters of the North Pacific Subtropical Gyre. Using metagenomics and quantitative transcriptomics, they monitored the temporal abundance and transcriptional activities of the most abundant double-stranded DNA viruses in the euphotic zone of the ocean and report synchronized diel coupling of viral and cellular replication cycles in both photoautotrophic and heterotrophic bacterial hosts. Moreover, dominant viruses persisted for exte nded time periods, which suggests that both core viral genomes and viral community structure are conserved over interannual periods.Thus, viruses are intrinsically synchronized with the daily and seasonal rhythms of marine microbial community processes.